The invention comprises a method and apparatus for concentrating and/or positioning particles or cells or similar.
A number of methods for concentrating particles or cells are very well known. Many frequently used methods involve centrifugation usually resulting in packing of the concentrated particles or cells at the bottom of a centrifuge tube when the medium is less dense than the particles or cells. In some circumstances this has disadvantages as it may be necessary to resuspend the particles or cells so that they may be further used. Furthermore closely packed particles or cells often adhere to one another or to the surface. One approach to overcoming these problems is to centrifuge using a concentration gradient or to centrifuge on to a small cushion of more dense medium. That approach has the disadvantage that the particles or cells then become mixed with a dense medium.
Other methods involve filtration which can also cause problems with dense packing of the particles or cells and/or drying out.
It is an object of the invention to provide a method for concentrating particles or cells and/or positioning these in a medium having a lower density than the density of the particles or cells, which does not involve packing of the particles or cells against a surface.
In broad terms in one aspect the invention comprises a method for concentrating and/or positioning particles or cells in a liquid medium comprising:
subjecting the particles or cells to an electric field to levitate the particles or cells within the medium by negative dielectrophoresis, and
heating the medium to cause convection currents within the liquid medium which concentrate or relocate the levitated cells within the medium.
More particularly the invention comprises a method for concentrating and/or positioning particles or cells comprising:
placing a liquid medium containing the particles and/or cells over a surface having an electrode array associated with the surface,
applying an alternating voltage to the electrode array to create an electric field above the surface within the medium to repel the particles or cells from the electrode array and thereby levitate the particles or cells above the surface, within the medium, by negative dielectrophoresis, and
heating the liquid medium so as to cause convection currents to circulate within the medium which concentrate or relocate the levitated cells within the medium.
In broad terms in another aspect the invention comprises a method for separating particles or cells in a liquid medium comprising:
subjecting the particles or cells to an electric field to levitate two or more different types of particles or cells within the medium to two or more different heights within the medium, and
heating the medium to cause convection currents within the liquid medium which concentrate or relocate the levitated cells within the medium.
More particularly the invention comprises a method for separating particles or cells comprising:
placing a liquid medium containing the particles and/or cells over a surface having an electrode array associated with the surface,
applying an alternating voltage to the electrode array to create an electric field above the surface within the medium to repel the particles or cells from the electrode array and which thereby levitates at least two different types of particles or cells to two or more different heights above the surface, within the medium, by negative dielectrophoresis, and
heating the liquid medium so as to cause convection currents to circulate within the medium which concentrate or relocate the levitated cells within the medium.
In broad terms in a further aspect the invention comprises apparatus for concentrating and/or positioning particles or cells in a liquid medium comprising:
means to subject the particles or cells to an electric field to levitate the particles or cells within the medium by negative dielectrophoresis, and
means to heat the medium to cause convection currents within the liquid medium which concentrate or relocate the levitated cells within the medium.
More particularly the invention comprises apparatus for concentrating and/or positioning particles or cells comprising:
a surface having an electrode array associated with the surface,
and means for containing a liquid medium containing the particles and/or cells over the surface,
means for applying an alternating voltage to the electrode array to create an electric field above the surface within the medium to repel the particles or cells from the electrode array and thereby levitate the particles or cells above the surface, within the medium, by negative dielectrophoresis, and
means for heating the liquid medium so as to cause convection currents to circulate within the medium which concentrate or relocate the levitated cells within the medium.
The method and apparatus of the invention may be used to concentrate and or position or reposition bacteria, fungi, protozoans or mammalian circulatory cells (e.g. from blood or lymph), viruses, inert particles such as polystyrene micro particles, which are often used as carriers for antibodies or other biologicals, nanoparticles, and similar, in immunology, diagnostics, or any other related or unrelated laboratory or industrial application. In this specification all of the above are for convenience intended to be encompassed herein by the expression xe2x80x9cparticles and cellsxe2x80x9d.
The concentration is due to two sorts of localisation of the particles: above the electrode plane and also within that horizontal plane. Vertical localisation arises because the particles are denser than the medium but are repelled from close approach to the electrodes by the electric field within the medium just above the electrode array. They are levitated by a force known as negative dielectrophoresisxe2x80x94see Pohl, HA (1978) Dielectrophoresis, Cambridge University Press.